Many existing wireless ad hoc networks were built with the assumption that every network node has a free and essentially unlimited power supply. In recent years, researchers have begun to think about battery-powered ad hoc networks. Several groups have begun work on ultra low-power radios suitable for use in low-energy nodes. Such ultra low-power radios have their receivers turned off most of the time because of the receivers' high power requirements. The best ultra low-power radio designs include a receiver that is powered by a small trickle of energy in a kind of “pager mode,” such that the receiver can be woken up by an incoming signal and can turn power on to a remainder of the receiver, for example, a processor, a memory, and the like.
Various network research teams have begun to think about how to create energy-conserving ad hoc networking protocols. One example includes scheduling when a given node is to transmit, such that nearby nodes may turn their receivers on at the scheduled time in order to receive the given node's transmission. This type of scheduling approach makes it possible for nodes to keep their receivers in a powered off state for long periods of time, for example, hours or days. As a result, it is difficult for a new node to enter the network because the existing network nodes with powered off receivers will not respond to transmissions from the new node. Consequently, the new node may not be able to learn the schedules used by the existing nodes in the network. An energy-conserving ad hoc network that allows new low-powered nodes to easily enter the network is needed.